function lemonadeChange(bills: number[]): boolean {
    let ten:number = 0;
    let five:number = 0;
    for(let b of bills){
        switch(b){
            case 5:
                five ++;
                break;
            case 10:
                five --;
                ten ++ ;
                break;
            case 20:
                ten ? (ten --,five--) : five -= 3;
                break;
        }
        if(five<0){
            return false;
        }
    }
    return true
};